This invention relates to a process for removing water from a non-volatile acid. More particularly, this invention relates to removing water from an alkanesulfonic acid.
Lower-alkanesulfonic acids, particularly methanesulfonic acid (MSA) and ethanesulfonic acid, have been found to be particularly useful reagents in the condensation reaction of phenol and chloroacetone to form 4,4'-dihydroxy-.alpha.-methylstilbene (DHAMS). Although MSA is more expensive than sulfuric acid, waste stream levels are substantially reduced when MSA is used; unlike sulfuric acid, the combination of phenol and MSA forms a homogeneous mixture below the temperature at which the condensation reaction is typically performed (about -15.degree. C.), thereby substantially reducing the requirement for waste-generating ancillary solvents. In view of the comparatively high cost of MSA, it would be desirable to find an economical means of dehydrating and recycling this reagent.
Methods for recovering acids are well known in the art. For example, U.S. Pat. No. 2,124,729 by Castner et al. discloses a reduced pressure, falling film evaporative method of removing water from water-containing acids. U.S. Pat. No. 2,711,388 by Mottern et al. discloses a flash distillation method for removing water from aqueous acids such as sulfuric acid and MSA. More recently, U.S. Pat. No. 4,450,047 by Malzahn and U.S. Pat. No. 4,938,846 by Constock et al. disclose reduced pressure, falling film evaporative methods for removing water from lower-alkanesulfonic acids.
It would be desirable to remove water from non-volatile acids, particularly MSA, under less rigorous conditions than those disclosed in the processes of the prior art. It would further be desirable to provide a method for the recovery and reuse of MSA in a process for preparing DHAMS.